1. Field of the Invention
This invention relates to a process for preparing aromatic polymers. More particularly it relates to a process for preparing conjugated aromatic polymers and electronic devices made with such polymers.
2. Description of the Related Art
Organic electronic devices are present in many different kinds of electronic equipment. In all such devices, an organic active layer is sandwiched between two electrical contact layers. Examples of organic electronic devices include devices that emit light, such as light-emitting diodes (LEDs) that make up displays. In LEDs, at least one of the electrical contact layers is light-transmitting so that light can pass through the electrical contact layer. The organic active layer emits light through the light-transmitting electrical contact layer upon application of electricity across the electrical contact layers.
It is well known to use organic electroluminescent compounds as the active component in light-emitting diodes. Simple organic molecules such as anthracene, thiadiazole derivatives, and coumarin derivatives are known to show electroluminescence. Several classes of conjugated aromatic luminescent polymers have also been disclosed. These include, for example, arylene vinylene polymers, such as poly(1,4-phenylene vinylene) and derivatives; polythiophenes, especially, poly(3-alkylthiophenes); poly(p-phenylenes); 2,7-poly(9,9-dialkylfluorenes); and copolymers thereof.
One method of preparing these polymers, particularly the arylene vinylene polymers, is to form soluble precursor polymers with thermally labile leaving groups. Heat treatment results in elimination of the leaving groups to form the conjugated polymer. Another route to these polymers is based on the Pd-catalyzed cross-coupling reacting between an aromatic boronic acid derivative and an aromatic halide, in the presence of an aqueous carbonate or bicarbonate base and an organic solvent. This route was first reported by Suzuki in Synthetic Communications, Vol. 11, No. 7, p. 513 (1981), and is commonly referred to as the “Suzuki method”. However, this procedure requires long reaction times in an oxygen-free atmosphere. Also, control of the molecular weight is difficult and thus reproducibility is poor. A modified Suzuki method was reported by Inbasekaran et al. in U.S. Pat. No. 5,777,070, in which a phase transfer catalyst was added to facilitate the reaction of the boronate anion with the Pd-aromatic halide complex. However, reaction times were still long. A second modified method was reported by Towns et al., in published PCT application WO 00/53656, in which an aromatic halide was reacted with an aromatic with a boron functional group in the presence of a Pd catalyst and an organic base in an amount sufficient to convert the boron functional group into —B(X)3— anionic groups. This reaction, although reportedly faster, still requires an oxygen-free atmosphere.
There is a continuing need for improved processes for preparing aromatic polymers.